Method of producing an analyzer electrode system for mass spectrometers



W. HANLEIN METHOD OF PRODUCING AN ANALYZER ELECTRODE SYSTEM FOR MASS SPECTROMETERS June 27, 1967 2 Sheets-5heet 1 Filed July 17, 1963 FIG. 1

FIG.2

FIGA

FIG. 3

June 27, 1967 w. HANLEIN METHOD OF PRODUCING AN ANALYZER ELECTRODE SYSTEM FOR MASS SFECTROMETERS Filed July 17, 1963 2 Sheets-Sheet 2 iii iiiif FIG. '5 7 FIG. 7

United States Patent Ofilice 3,328,l4 Patented June 27, 1967 3,328,145 METHOD ()F PRODUCING AN ANALYZER ELEC- TRODE SYSTEM FOR MASS SPECTRGMETERS Walter Hanlein, Erlangen, Germany, assiguor to Siemens- Schuckertwerke Aktiengesellschait, Berlin-Siemensstad't, Germany, a corporation of Germany Filed July 17, 1963, Scr. No. 295,631 Claims priority, application Germany, July 21, 1962, S 843,532 3 Claims. (till. 65-60) My invention relates to mass spectrometers of the type known from U.S. Patents 2,939,952 and 2,950,389, in which ions of different specific charges .are shot, from an ion source, between a number of elongated field electrodes that extend substantially parallel to the trajectory direc tion and are kept at an electric potential, generally composed of a high-frequency alternating component and a direct component, so that certain ions, depending upon their mass, are deflected onto the analyzer electrodes whereas others pass through the electrode field and ultimately impinge upon a collector electrode.

As a rule, four metal rods are employed as electrodes of the analyzer system. The distance between the individual electrode rods as well as the diagonal spacings must be accurately identical. The system must also be free of any skew or twist. The mechanical production of such systems from four individual rods is extremely difficult. It also hapens that the, electrode rods in such systems, particularly in mass filters for very low partial pressures, requiring heating to temperatures up to about 450 C., are apt to become distorted during use although their mutual arrangement was accurate originally.

It is an object of my invention to facilitate the production of a twist-free analyzer system of high accuracy for mass spectrometers of the above-mentioned type, such as a mass filter according to Paul as described in the abovementioned Patent 2,939,952. An object of my invention is also to devise a relatively simple manufacturing process that results in a mass-spectrometer analyzer system of improved stability so as to assure accurate dimensions and absence of internal twist after prolonged periods of operation.

According to my invention, a twist-free assembly of elongated and symmetrically parallel electrode rods for a mass-spectrometer analyzer system is produced by placing or pulling a tube of electrically poorly conducting, softenable material coaxially over a core mold whose perimetric surface is provided with grooves that extend parallel to the core axis. Thereafter, the material of the tube, then jacketing the core, is softened so that it enters into the grooves and fits snugly into them. After hardening of the material, the tube portions then protruding inwardly into the grooves form properly correlated surfaces corresponding in contour and extent to the electrode surfaces to be ultimately obtained. After the core mold is removed, these protruding inner surfaces are metallized so that they are available as analyzer electrodes which are rigidly spaced relative to each other at the proper mutual and diagonal distances. Suitable as electrically poorly conducting material for the tube is glass or synthetic plastic, preferably tetrafluoroethylene as available in the trade under the name Teflon.

The core mold, instead of being provided with four grooves, may be given any other desired even number of grooves uniformly distributed about the periphery. The cross section of the grooves is inwardly convex such as approximately semicircular or parabolic. A metallic body, preferably of stainless steel is suitable as a core mold. This core body is preferably ground and polished. The grooves can be produced in any suitable manner, for example by grinding them into the body. The material of the core mold should have a greater coefiicient of thermal expansion than the material of the softenable tube material,

as is the case with the preferred selection of substances mentioned in the foregoing.

After placing the tubular body onto the core mold, the heating and resulting softening of the tube material preferably is accomplished by inductive heating of the metallic core mold. During softening of the material, electric current-supply leads may also be attached to the inwardly protruding rod-shaped portions of the tube. Prior to softening and during softening, the tube can 'be closed and evacuated.

The invention Will be further described with reference to the accompanying drawings, in which:

FIG. 1 is explanatory and shows schematically a complete mass-spectrometer apparatus of the above-mentioned type.

FIG. 2 shows schematically a mutual arrangement of four analyzer electrodes in such a mass filter.

FIG. 3 is a cross section along line A-B in FIG. 4 through a core mold covered by a glass tube during a stage of the process according to the invention.

FIG. 4 is a lateral view of a core mold fused into a glass tube.

FIG. 5 shows the same fused-off glass tube with an enclosed core mold but surrounded by an induction heater winding as used during the softening stage in the process according to the invention.

FIG. 6 shows schematically and in perspective a glass tube, cut to proper length and provided with four grooves, this tube having metallized inner surfaces and thus constituting the product of the method.

FIG. 7 shows separately a portion of the glass tube with an electric conductor wire attached to one of the analyzer electrodes.

FIG. 8 is a plan view of the portion shown in FIG. 7.

In FIG. 1, a spectrometer tube 1 has an envelope 5 containing an ion source 2, and a group of rod-shaped deflector electrodes 3 each having a circular cross section, L0- catcd at the end of the ion-beam path is a cup-shaped collector electrode 4. The ion source 2 and the collector electrode 4 are coaxially spaced from each other and thus define a center axis for the ion beam issuing from the source 2 toward the electrode 4. The electrode rods 3 are uniformly distributed about the ion-beam axis and extend parallel thereto. A total number of four such electrodes rnav be used.

The above-mentioned envelope 5 of the cell 1 is vacuumtightly sealed and has a nipple or neck 6 connected with a tank 7 containing the gaseous mixture to be investigated. The rod electrodes 3 are electrically connected in pairs to a high-frequency generator 8 which supplies electric energy of suitable voltage and frequency. The current due to the ions impinging upon the collector 4 is amplified by an amplifier 9 and supplied to a recorder 10 or other indicating or measuring device. Another measuring instrument 10' is provided for supervising the electron emission of the cathode in the ion source 2.

During operation, a beam of ions is continuously being extracted from the source 2 and is directed toward the collector 4. However, only the ions of a given specific electric charge, or within a given range of charges, can reach the collector 4. Those ions which have different specific charges travel on instable, pendulous paths and thus impinge upon the deflector electrodes 3, thus being filtered out of the mixture. This is more fully explained in the above-mentioned patents as well as U.S. Patent No. 3,075,- 076, and U.S. patent application Ser. No. 256,169, filed Feb. 4, 1963.

The requirements to be met by the analyzer system will be understood from the diagram shown in FIG. 2. The four analyzer rods 3- are identified as rods 11, 12, 13 and 14 in FIG. 2. The four rods, as seen in FIG. 2, are arranged at the corners of a square. The mutual spacing a between each two rods must be accurately equal to the spacing between any other two rods, and the length of the diagonal spacings b must also be accurately identical. These dimensions must also be the same over the entire axial length of the analyzer system. The accuracy heretofore attainable by mechanical adjustment amounts to a few multiples of 10 microns; however, the system may become skewed or twisted during heating-up of the spectrometer.

As described above, an analyzer system satisfying these exacting requirements is produced according to the invention in the manner described presently with reference to FIGS. 3 to 8. According to FIG. 3, a glass tube 21 of originally cylindrical shape is used. A metal core mold 23, accurately machined, ground and polished is axially inserted into the glass tube. At the four locations denoted by 22, the mold is provided with grooves of semicircular cross section. The mold is preferably made of Cr-Ni steel or other stainless alloy steel. According to another embodiment of the invention the grooves are parabolic in cross section.

As shown in FIG. 4, the glass tube is given a constriction above and below the mold 23 and then fused off. When the second end of the glass tube is being heated, softened and molded to the illustrated shape in order to be fused off, the interior of the tube may be connected to a vacuum pump, so that the heated glass tube is pulled tightly about the core mold. If desired, one end of the glass tube may also remain open and may then be connected with a vacuum pump for the duration of the entire molding process.

The glass tube 21 with the enclosed mold 23 is then placed in a furnace, and the entire assembly is heated to a temperature slightly above the transformation point of the glass. After some time, the glass enters into the grooves 22 of the mold 23 (FIG. 3). During subsequent cooling, the mold 23 contracts more strongly than the glass tube, so that when the ends of the glass tube are severed off, the mold can be pulled out of the remaining glass tube. The tube then has four hollow-cylindrical portions that protrude inwardly along the entire length of the cut-off tube as is apparent from FIG. 6. The inner surfaces of these protruding portions are then metallized or mirrored, for example by vaporizing gold onto these surfaces or depositing gold by cathode spattering. In FIG. 6 the metallized inner surfaces on the projections are identified by shading and denoted by 25. In this manner, a twist-free analyzer system of accurate dimensions is produced, which retains the original dimensions virtually during the lifetime of the mass spectrometer.

The above-described heating operations required for softening the glass tube can also be effected, in part or entirely, by means of induction heating. For this purpose, the tube 21 is shown in FIG. surrounded over substantially its entire length by an induction heater coil 24 which during operation is energized by high-frequency current.

The attachment of the electric conductors to the rodshaped protruding portions of the tubular structure is effected by fusing them in during the softened condition of the structure in the manner described with reference to FIGS. 7 and 8. In order to have the electric leads impose the slightest possible effect upon the electric analyzer field of the mass spectrometer, the conductors attached to the metallized portions should protrude as little as possible from the active, convex surfaces of the electrodes. For this purpose, the ends should be pressed or otherwise embedded into this surface so that they lie flush therewith or stay beneath the convex surface, this being not shown in FIGS. 7 and 8. In the illustrated embodiment the conductor wire 26 has a circular cross section. It passes through a generally conical body of glass 27 which is first attached to the wire 26 before the glass cone 27 is fused to the tubular structure 21. The wire, consisting of platinum or any other material used for lead-ins passing through glass, has its outer end bent in the reverse direction and also fused together with a glass, plastic or other moldable material being used for the tubular structure. The metallization is preferably placed upon the protruding portions of the tubular structure after the conductor wires are attached. As a result, the metallization also takes care of providing for a good metallic contact between the fused-in wires and the vapor-deposited metal layer that is ultimately effective as the electrode surface proper.

While an embodiment of the invention has been described in detail, it will be obvious to those skilled in the art that the invention may be embodied otherwise without departing from its spirit and scope.

I claim:

1. The method of producing a twist-free assembly of elongated and symmetrically parallel electrode rods adjacent ones of which are equidistantly spaced from each other along their entire lengths and opposite ones of which are equidistantly spaced from each other along their entire lengths, the distances between each set of adjacent rods being the same and the distances between each set of opposite rods being the same, said rods being utilized as the deflector electrodes of the analyzer system of a mass spectrometer, said method comprising the steps of placing a tube of electrically poorly conducting and softenable material coaxially over an elongated core mold having grooves parallel to the axis of the mold formed therein, softening the tube material to conform its shape to that of the grooves, hardening the material so that the part in the grooves forms inwardly protruding rigid tube portions, removing the mold from the tube, and metallizing the inner surfaces of the protruding portions of the tube whereby the metallized portions are adapted for use as the deflector electrode rods.

2. The method of producing a twist-free assembly of elongated and symmetrically parallel electrode rods adjacent ones of which are equidistantly spaced from each other along their entire lengths and opposite ones of which are equidistantly spaced from each other along their entire lengths, the distances between each set of adjacent rods being the same and the distances between each set of opposite rods being the same, said rods being utilized as the deflect-or electrodes of the analyzer system of a mass spectrometer, said method comprising the steps of placing a tube of electrically poorly conducting and softenable material coaxially over an elongated core mold having four peripherally spaced grooves parallel to the axis of the mold surface and uniformly spaced from each other formed therein, softening the tube material to conform its shape to that of the grooves, hardening the material so that the part in the grooves forms inwardly protruding rigid tube portions, removing the mold from the tube, and metallizing the inner surfaces of the protruding portions of the tube whereby the metallized portions are adapted for use as the deflector electrode rods.

3. The method of producing a twist-free assembly of elongated and symmetrically parallel electrode rods adjacent ones of which are equidistantly spaced from each other along their entire lengths and opposite ones of which are equidistantly spaced from each other along their entire lengths, the distances between each set of adjacent rods being the same and the distances between each set of opposite rods being the same, said rods being utilized as the deflector electrodes of the analyzer system of a mass spectrometer, said method comprising the steps of placing a tube of electrically poorly conducting and softenable material coaxially over an elongated core mold having grooves of semicircular cross section extending parallel to the axis of the mold formed therein, softening the tube material to conform its shape to that of the grooves, hardening the material so that the part in the grooves forms inwardly protruding rigid tube portions, removing the mold from the tube, and metallizing the inner surfaces of 5 the protruding portions of the tube whereby the metallized 2,556, 864 portions are adapted for use as the deflector electrode rods. 2,822,501 2,874,325 References Cited 21,933,634 UNITED STATES PATENTS 5 2,945,327 4/1919 Kueppers 6 5-108 395426 2/192'2 Crocker 2925.18 5/ 1926 Houskeeper 65-108 X 4/1934 Miesse 29- 2518 10/ 1940 Langmuir 65-60 X 10/1944 White 65-155 X 6 Apker 31 3- 3f Poulter 65-110 l Voreaux 313-35 Lederer 65-60 j Malm et a1 65155 I Camarata 65155 I DONAL-L H. SYLVESTER, Primary Examiner.

R. NILSON, Examiner.

H. S. MILLER, F. W. MIGA, Assistant Examiners. 

1. THE METHOD OF PRODUCING A TWIST-FREE ASSEMBLY OF ELONGATED AND SYMMETRICALLY PARALLEL ELECTRODE RODS ADJACENT ONES OF WHICH ARE EQUIDISTANTLY SPACED FROM EACH OTHER ALONG THEIR ENTIRE LENGTH AND OPPOSITE ONES OF WHICH ARE EQUIDISTANTLY SPACED FROM EACH OTHER ALONG THEIR ENTIRE LENGTHS, THE DISTANCES BETWEEN EACH SET OF ADJACENT RODS BEING THE SAME AND THE DISTANCES BETWEEN EACH SET OF OPPOSITE RODS BEING THE SAME, SAID RODS BEING UTILIZED AS THE DEFLECTOR ELECTRODES OF THE ANALYZER SYSTEM OF A MASS SPECTROMETER, SAID METHOD COMPROSING THE STEPS OF PLACING A TUBE OF ELECTRICALLY POORLY CONDUCTING AND SOFTENABLE MATERIAL COAXIALLY OVER AN ELONGATED CORE MOLD HAVING GROOVES PARALLEL TO THE AXIS OF THE MOLD FORMED THEREIN, SOFTENING THE TUBE MATERIAL TO CONFORM ITS SHAPE TO THAT OF THE GROOVES, HARDENING THE MATERIAL SO THAT THE PART IN THE GROOVES FORMS INWARDLY PROTRUDING RIGID TUBE PORTIONS, REMOVING THE MOLD FROM THE TUBE, AND METALLIZING THE INNER SURFACE OF THE PROTRUDING PORTIONS OF THE TUBE WHEREBY THE METALLIZED PORTIONS ARE ADAPTED FOR USE AS THE DEFLECTOR ELECTRODE RODS. 